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Boston Dynamics, a Waltham company that three years ago introduced the four-legged BigDog robot, a beast of burden designed to traverse rough terrain, is unveiling its newest creation: an improved version of a walking machine that is shaped like a human being.

The mule-like BigDog created a sensation three years ago, when it was shown climbing snow-covered hills, keeping its balance on slippery ice, and withstanding the kicks and shoves of its engineer creators. Boston Dynamics’ video of BigDog in action has attracted more than 12 million viewers on YouTube.

The company may have another robotic sensation: PETMAN, a two-legged, 180-pound machine nearly six feet tall. Boston Dynamics, which has created a slew of robots for the military over the years, is expected today to publicly unveil the first video of the nearly fully developed PETMAN, power-walking on a treadmill in the company’s labs.

PETMAN, an acronym for Protection Ensemble Test Mannequin, does not look like Arnold Schwarzenegger, who played the Terminator killing machine in the first of a series of movies. For one thing, PETMAN still lacks a head, and it can’t say “Hasta la vista, baby.’’

But it can walk like a person, and it’s set for possible delivery next year to the military, which plans to use it for testing clothing and headgear intended to protect soldiers from chemical warfare agents.

Over the past decade, the military has been investing heavily in robotic aircraft and other devices, some of which have been deployed in Afghanistan and Iraq. Unmanned Predator aircraft, which can monitor and fire at ground targets, are perhaps the best known.

Some military analysts question the Pentagon’s long-term, multimillion-dollar investments in robotic products, but it appears PETMAN and other products are accelerating the progress in robotic technology.

“We’re absolutely turning a corner in robotics,’’ said Marc Raibert, president of 19-year-old Boston Dynamics.

There is something of a robotics sector in Massachusetts, including Boston Dynamics and iRobot Corp. in Bedford. It, too, has produced robots for the military, such as its surveillance and bomb-detection PackBot, as well as robotic consumer products that clean floors and gutters.

Chris Anderson, president of the industry group Massachusetts High Technology Council, said companies like Boston Dynamics are important to the state’s economy. “It’s extremely significant to the innovation ecosystem here,’’ he said.

Boston Dynamics, which was founded by engineers from the Massachusetts Institute of Technology, has worked for years on products such as LittleDog and BigDog carrying robots, both funded by the military’s Defense Advanced Research Projects Agency.

Now, via a $33 million contract with the agency, the company has developed the four-legged successor to BigDog: AlphaDog, officially known as the Legged Squad Support System, or LS3.

Next year, Boston Dynamics expects to deliver to the military two “walk out’’ versions of the LS3, which is bigger, stronger, and faster than BigDog.

The ultimate goal: to get some sort of four-legged robotic vehicle into combat to deliver ammunition and other crucial materials to soldiers in hard-to-reach areas. In effect, AlphaDog, or a variation of it, would act as a mechanical pack mule for soldiers.

AlphaDog can carry a 400-pound payload, travel up to 20 miles, and move at 7.5 miles per hour.

Unlike BigDog, it can perform all three functions at the same time, Raibert said, and is “10 times quieter.’’ BigDog sounds like a whirring chainsaw, he said.

AlphaDog will have another advanced feature: Its sophisticated sensor system will allow it to operate without manual controls. It will automatically follow a human squad leader step for step, curling around trees and over fallen obstacles.

“It’s designed to follow soldiers from behind, like in a caravan,’’ Raibert said. “There’s a big qualitative increase in its capabilities, compared to BigDog.’’

But PETMAN - the human-form robot was developed as part of a $26.5 million program for the Army - may be its most sensational robot yet.

Boston Dynamics had previously released a video showing a prototype robot walking on two legs, but the device did not have shoulders, arms, or a chest.

PETMAN has been through preliminary tests in preparation for use next year as part of an anti-chemical-warfare program developed by the Pentagon. Because it can walk, turn, and twist like a person, PETMAN will serve as a stand-in for humans when it is doused with noxious chemicals in tests.

“The PETMAN robot will enable a kind of lifelike testing of protective clothing that the [Pentagon] has long sought and never had,’’ said Dr. Robert Playter, vice president of engineering at Boston Dynamics.

Douglas Macgregor, a retired Army colonel and executive vice president at the national security consulting firm Burke-Macgregor Group, in Virginia, said companies like Boston Dynamics are “no doubt producing brilliant technologies’’ for the military.

“I think unmanned systems have huge potential,’’ Macgregor said, though he questioned whether all of the robotic products at Boston Dynamics will ever be used in real military situations. “We have to be careful about these expenditures,’’ he said.

In a statement, Lieutenant Colonel Joseph Hitt, program manager at the Defense Advanced Research Projects Agency, said robotic projects are intended to be door-openers for future innovations as well as pragmatic.

Another question: What do billions of dollars in potential Pentagon budget cuts mean for the robotics?

Last week, iRobot said it was reducing its payroll by 8 percent of its workforce, or 55 employees - including 44 in Massachusetts - in anticipation of defense spending reductions. Congress is examining ways to reduce the nation’s budget deficits.

Boston Dynamic’s Raibert, whose company has grown to 85 people from about 55 a few years ago, said he is aware of skepticism about the military future for robotics - and aware of potential defense industry cuts.

But he expressed confidence that robotic vehicles, aircraft, and other products are part of the military’s future, and that they have commercial potential, as well.

He said he envisions robots such as AlphaDog being used to help fight fires and carry commercial equipment to difficult-to-reach locations.

Robots like PETMAN may later be used commercially as stand-ins for humans in dangerous assignments, such as working in nuclear power plants.